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Abstract:

A method is described for transmitting a multimedia stream from a first
terminal and receiving an associated second multimedia stream at a second
terminal. The first and second terminal are connected to at least one
gateway for enabling the transmission of the stream and the receiving of
the associated stream. The method comprises: initiating the exchange of
first multimedia session information between the first terminal and the
gateway, using a first protocol; providing a trigger to the second
terminal to initiate the exchange of second multimedia session
information between the second terminal and the gateway, using a second
protocol; in response to providing the trigger, the second terminal
initiating the exchange of second multimedia session information between
the second terminal and the gateway, using a third protocol; transmitting
a first multimedia stream from the first terminal and receiving a second
associated multimedia stream at the second terminal.

Claims:

1-13. (canceled)

14. A method, wherein a gateway is capable of communicating with a first
terminal and a second terminal, the method comprising: the gateway or the
first terminal using a first protocol to exchange first media session
information between the first terminal and the gateway, wherein the
exchange of the first media session information sets up a first media
stream from the first terminal; the second terminal using a second
protocol to receive a trigger provided by the gateway or first terminal,
wherein the trigger is to initiate an exchange of second media session
information between the gateway and the second terminal; in response to
receiving the trigger, the second terminal using a third protocol to
initiate the exchange of the second media session information between the
gateway and the second terminal, wherein the exchange of the second media
session information sets up a second media stream in which the second
terminal participates; and the second terminal receiving the second media
stream, wherein the second media stream is associated with the first
media stream.

15. The method according to claim 14, wherein the exchange of the first
media session information comprises: the gateway providing to the first
terminal at least part of the second media session information.

16. The method according to claim 14, wherein the exchange of the second
media session information comprises: the gateway providing to the second
terminal at least part of the first media session information.

17. The method according to claim 14, wherein the exchange of the first
media session information comprises: the gateway receiving, from the
first terminal, an identifier of the second terminal.

18. The method according to claim 17, further comprising: before using
the second protocol to provide the trigger to the second terminal, the
gateway resolving the identifier of the second terminal into a network
address of the second terminal.

19. The method according to claim 18, wherein providing the trigger to
the second terminal comprises the gateway transmitting the trigger to the
resolved network address of the second terminal.

20. The method of claim 14, wherein the third protocol is different from
the second protocol.

21. The method of claim 14, wherein the first multimedia stream is the
second multimedia stream.

22. The method of claim 14, wherein the trigger serves to inform the
second terminal of availability of a new multimedia stream.

23. The method of claim 14, wherein the first protocol is a peer-to-peer
protocol.

24. The method of claim 14, wherein the third protocol is a client-server
protocol, and wherein the second receiving terminal has client
capabilities of the third protocol and not server capabilities of the
third protocol.

25. The method of claim 14, wherein the trigger comprises a network
address of the gateway.

26. The method of claim 25, wherein the network address is a URI or a URI
reference.

27. The method of claim 14, wherein the first protocol and the second
protocol are identical.

28. The method of claim 27, wherein the first protocol and the second
protocol are the Session Initiation Protocol (SIP).

29. The method of claim 14, wherein the gateway is configured to
associate the first multimedia session information with the second
multimedia session information.

30. An article of manufacture including a non-transitory
computer-readable medium, having stored thereon software instructions
that, if executed by a computing device, cause the computing device to
perform operations comprising: using a first protocol to initiate an
exchange of first media session information between a first terminal and
a gateway, wherein the exchange of the first media session information
sets up a first media stream from the first terminal; using a second
protocol to provide a trigger to a second terminal, wherein the trigger
is to initiate an exchange of second media session information between
the gateway and the second terminal; using the second protocol to conduct
the exchange of the second media session information between the gateway
and the second terminal, wherein the exchange of the second media session
information sets up a second media stream in which the second terminal
participates; and using the first protocol to transmit a response to the
first terminal, wherein the response causes the first terminal to begin
transmission of the first media stream.

31. A gateway comprising: a communication interface; and memory that
stores software instructions that, when executed by the gateway, cause
the gateway to: (i) exchange first multimedia session information with a
first terminal using a first protocol, wherein the exchange of the first
media session information sets up a first media stream from the first
terminal, (ii) provide a trigger to a second terminal, wherein the
trigger is provided using a second protocol, in response to which the
second terminal is able to initiate the exchange of second multimedia
session information with the gateway, and (iii) exchange second
multimedia session information with the second terminal, using a third
protocol, wherein the third protocol is different from the first
protocol, wherein the exchange of the second media session information
sets up a second media stream in which the second terminal participates.

32. The gateway of claim 31, wherein the gateway is configured to connect
to a first terminal supporting a first protocol and to a second terminal
supporting a second protocol, wherein the first protocol is Session
Initiation Protocol (SIP) and the second protocol is Real Time Streaming
Protocol (RTSP), wherein the first terminal is an originating SIP client
of a user at a user side, wherein the gateway acts as a terminating SIP
client, wherein the gateway is configured to confirm that the gateway is
able to receive a multimedia session from the user and to provide the
first terminal with multimedia session information, wherein the second
terminal is an RTSP client, wherein the gateway acts as an RTSP server on
behalf of the user, wherein the second terminal uses RTSP for session
control, and wherein the gateway is configured to inform the second
terminal that an incoming session is pending and notify the RTSP client
to connect to an RTSP server function of the gateway.

33. The gateway of claim 31, wherein the gateway is configured to
transmit a notification message to the second terminal in response to an
invitation of the first terminal, in order to activate the second
terminal to set up the second multimedia session between the second
terminal and the gateway.

34. The gateway of claim 31, wherein the gateway is embedded in an IP
Multi-Media Subsystem (IMS) network architecture, wherein the first
protocol is Session Initiation Protocol (SIP), wherein the third protocol
is Real Time Streaming Protocol (RTSP), the IMS network architecture
comprising a service-control-function component and a media-function
component, wherein the memory of the gateway is distributed in the IMS
network architecture, such that: exchanging the first multimedia session
information is handled by the service-control-function component within
the IMS network architecture; triggering the second terminal is
controlled by the service-control-function component within the IMS
network architecture; and exchanging second multimedia session
information is handled by the media-function component within the IMS
network architecture.

35. The gateway of claim 31, wherein the gateway is configured to
associate the first multimedia session information and the second
multimedia session information with each other.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] The present patent application is a continuation of U.S. patent
application Ser. No. 12/808,665, entitled "Method and system for
transmitting a multimedia stream," filed Jun. 16, 2010, which is a
national stage entry of PCT/EP2008/11014, filed Dec. 22, 2008, which
claims priority to U.S. Provisional Patent Application Ser. No.
61/008,644, filed Dec. 21, 2007. The full disclosure of U.S. patent
application Ser. No. 12/808,665 is incorporated herein by reference.

FIELD OF THE INVENTION

[0002] The invention relates to a method and a system for transmitting a
multimedia stream from a first terminal to a second terminal. In
particular, the invention relates to a method and system for transmitting
a first multimedia stream from a first terminal and receiving a second
associated stream at a second terminal. The invention further relates to
a gateway and a device for use in such system.

BACKGROUND OF THE INVENTION

[0003] IP Multi-Media Subsystem (IMS) defined by the 3GPP and 3GPP2
standards open the door to a whole range of new multimedia services, such
as Voice over IP (VoIP) and IPTV. The IMS service architecture enables to
combine multimedia services of various types.

[0004] One type of services may enable viewers at home to participate
real-time in a live TV show using e.g. a webcam at home. The multimedia
streams generated by the webcam are transported from the home-located
user over an IP network to the TV studio using the Real-time Transport
Protocol (RTP). In an IMS based architecture such multimedia streaming
sessions between clients are set up using the Session Initiation Protocol
(SIP), whereas the Real Time Streaming Protocol (RTSP) is typically used
for streaming multimedia content from a server to a client.

[0005] Systems that provide an interface between SIP and RTSP domains,
usually referred to as SIP-RTSP gateways, are known in the art. Within
ETSI TISPAN Standardization (WI2048, TS 182 027) an architecture is
proposed in which a terminal, comprised in a device such as for example a
set-top box, a personal computer, a personal digital assistant (PDA) or a
mobile telephone with multi-media capabilities, uses SIP to set up a
multimedia session with a selected content provider. After establishment
of the session, RTSP is used to select, retrieve and control the streamed
content. Further, the University of Colombia (Kundan Singh and Henning
Schulzrinne, "Unified Messaging using SIP and RTSP", IP Telecom Services
Workshop, September 2000, Atlanta, Ga., US) has developed a SIP-RTSP
Gateway for multimedia unified messaging.

[0006] These systems use SIP and RTSP clients at the user side and SIP
clients and RTSP servers in the network, thereby enabling a user to
initiate the set up multimedia session in which multimedia content is
streamed from the RTSP servers to the user.

[0007] Another gateway system that may be used to stream multimedia
between different protocol domains is described in TAKEI K ET AL "Design
of gateway system between different signaling protocols of the multimedia
session on the internet" INFORMATION NETWORKING, 2001. PROCEEDINGS.
15TH INTERNATIONAL CONFERENCE ON 31 JANUARY-2 FEBRUARY, PISCATAWAY,
NJ, USA, IEEE, 2001, PAGES 297-302, ISBN: 0-7695-0951-7/01. This system
is used to interwork the SIP and the H323 protocol domains. Both
protocols are peer-to-peer type protocols and allow for bidirectional
set-up/initiation of sessions.

[0008] One problem related to these known systems is that they do not
provide all the functionality needed for the above mentioned services,
which require the user to initiate the set up a multimedia session such
that user-generated content is streamed from the user (the
transmitting-end) to the studio (the receiving-end), whereby the studio
may want to control the stream of user generated content. A known
protocol for controlling a stream is RTSP, whereby the receiving-end,
with RTSP client functionality, may be able to pause, or forward or
backward a stream, or play a stream at a different speed. If the
transmitting-end on the other hand is only capable of using the SIP
protocol for setting up and maintaining the multimedia streaming session,
the mentioned services cannot be realized with the known prior art
systems, since the SIP protocol does not provide the means for
controlling a stream in the way that for instance the RTSP protocol is
capable of.

[0009] Another problem related to the streaming of multimedia, that may
arise with prior art systems, is that when the receiving-end is only
equipped with client functionality of a client-server type of protocol
for receiving multimedia, it may only be capable of initiating a
multimedia session. If the transmitting-end, using for example a
peer-to-peer type of protocol, such as the SIP protocol, wants to
initiate a multimedia streaming session, the receiving-end is not capable
to respond to such an invitation. Prior-art systems, such as the known
SIP-RTSP gateways and the known SIP-H323 gateways do not provide a
solution for this problem.

[0010] A variety of additional problems may arise with prior art systems,
when the user generated multimedia has to be streamed to a multiple of
receiving-ends. These receiving-ends may all have different capabilities
or preferences when it comes to receiving a multimedia stream. One
receiving-end may want to receive a live stream, whereas the other may
want to be able to control the stream as described above. Additionally
these preferences and capabilities, as well as the network addresses of
the receiving-ends, may not be known to the transmitting-end.

SUMMARY OF THE INVENTION

[0011] It is an object of the invention to reduce or eliminate at least
one of the drawbacks known in the prior art and to provide a method and
system for transmitting a first multimedia stream from a first terminal
and receiving a second associated multimedia stream at a second terminal.

[0012] In an embodiment the first and second terminal are connected to at
least one gateway for enabling the transmission of the first multimedia
stream and the receiving of the second associated stream. The method
comprises the steps of:

[0013] initiating the exchange of first
multimedia session information between the first terminal and the
gateway, using a first protocol;

[0014] providing a trigger to the second
terminal to initiate the exchange of second multimedia session
information between the second terminal and the gateway, using a second
protocol;

[0015] in response to the providing of the trigger, the second
terminal initiating the exchange of second multimedia session information
between the second terminal and the gateway, using a third protocol, the
third protocol being different from the second protocol;

[0016]
transmitting a first multimedia stream from the first terminal and
receiving a second associated multimedia stream at the second terminal.
The method thus allows the user of a first terminal to transmit a
multimedia stream of real-time user-generated content to a second
terminal, whereby the first terminal uses a different multimedia protocol
to set up a multimedia stream as that the second terminal uses to receive
the associated multimedia stream.

[0017] In the method according to the embodiment a gateway is capable of
connecting a first terminal supporting a first protocol, e.g. SIP, to a
second terminal supporting a different (third) protocol, e.g. RTSP.
Towards the first terminal, i.e. the (originating) SIP client at the user
side, the gateway acts as (terminating) SIP client. The gateway exchanges
information about the specifications of the first multimedia session with
the first terminal. In the first multimedia session a multimedia stream
is transmitted from the first terminal. Towards the second terminal, i.e.
the RTSP client, the gateway acts as RTSP server on behalf of the user,
whereby the second terminal uses RTSP for exchanging information about
the specifications of the second multimedia session with the gateway. In
the second multimedia session a multimedia stream is received by the
second terminal.

[0018] The second terminal is triggered, using a second protocol that is
different from the protocol used by the second terminal to exchange
second multimedia session information, informing the second terminal of
the availability of a new multimedia stream and activating the RTSP
client to connect to the RTSP server function of the gateway. Optionally
the activation of the RTSP client may occur only after approval of the
user of the second terminal. The approval step is then simply part of the
fully automated process.

[0019] The gateway acts both as a SIP client and RTSP server and may
provide a trigger to the second terminal for connecting the second
terminal to the gateway. The invention is based on the idea that the
trigger is provided using a different protocol then the protocol used by
the second terminal to arrange the receipt of multimedia. This idea is
based on the insight that some protocols are only capable of initiating a
multimedia session in one direction. The trigger (message) ensures that
SIP clients from the user and RTSP clients from the studio can be
connected in order to enable user-generated content to be transmitted
from the first terminal to the second terminal.

[0020] In a further embodiment of the method according to the invention,
the exchange of first multimedia session information comprises the
providing to the first terminal of at least part of the second multimedia
session information and whereby transmitting of the first multimedia
stream from the first terminal is started in response to said providing.
This has the advantage of providing additional flexibility to the method.
It is no longer the gateway that supplies preconfigured specifications of
both related multimedia sessions to the terminals involved in the
transmitting and receiving of the stream, but the gateway may use
(requested by) settings from the second receiving terminal, and supply
these to the first, transmitting, terminal. Vice versa, and for the same
benefit, the gateway may use (requested by) settings from the first
transmitting terminal, and supply these to the second, receiving,
terminal. In both situations the transmitting, respectively receiving of
multimedia streams may only start after the exchange of these settings.

[0021] In an embodiment of the method, the first protocol is a peer to
peer type protocol, preferably the Session Initiation Protocol (SIP). The
advantage of the peer-to-peer protocol is that both sides may initiate
the set-up of a streaming session. So in the invention, it may be the
first terminal offering a multimedia stream or it may be the gateway
first requesting the first terminal to offer a multimedia stream. The SIP
protocol is a very commonly used protocol in multimedia sessions, and
therefore a lot of devices and network architecture support this
protocol.

[0022] In a further embodiment of the method the third protocol is a
client-server type protocol, preferably the Real Time Streaming Protocol
(RTSP). Typically a client-server type of protocol is a protocol that is
designed to support only one way initiation of the set up of a multimedia
session. Only the client can typically initiate the set-up. Therefore the
invention is advantageously used when the second receiving terminal has
only client capabilities of such a protocol and therefore is unable to
receive an invitation via such a protocol. The use of the RTSP protocol,
may be advantageous, when the receiving second terminal wants to control
the incoming stream and use the special control options of this protocol.

[0023] In a further embodiment of the method, the step of providing a
trigger to the second terminal is initiated by the gateway. Having the
gateway and not for example the first terminal provide the trigger, may
be advantageous when the first terminal does not have the right trigger
capabilities, does not know how to reach the second terminal, and in case
of a multiple of receiving terminals, that need to be reached.

[0024] In yet a further embodiment of the method, the trigger comprises a
network address, preferably an URI or URI reference, of the gateway. This
may be advantageous, if the second terminal is not configured with a
default address, or the default (proxy) address normally used for
receiving multimedia streams is not applicable.

[0025] In another embodiment of the method, the exchange of first
multimedia session information comprises the provisioning of an
identifier of the second terminal to the gateway. This may be
advantageous, if it is the gateway that provides the trigger to the
second terminal. In that situation, it is the gateway that needs to be
able to identify the address of the second terminal to be reached.

[0026] In a further embodiment of the method, the method comprises the
addition step of resolving the identifier of the second terminal into a
network address, before provisioning of the trigger to the second
terminal. This may be the situation, when the trigger is sent by the
gateway and the identifier does not comprise of a network address of the
second terminal. The identifier may be a closed user group ID, in which
case all network addresses of all receiving terminals need to be
identified first.

[0027] In another embodiment according to the method, the first and the
second protocol are identical. This simplifies the implementation of the
invention. A situation like this may occur when the receiving terminal
has both RTSP and SIP client capabilities. The trigger may then be
provided using the SIP protocol, whereas the initiation and set up of the
receipt of the multimedia stream may be done, using the RTSP client, thus
enabling control functionalities (trickplay) that SIP lacks.

[0028] In another embodiment of the method, the second associated
multimedia stream is a multicast stream. This may be advantageous when a
multiple of receiving terminals may be offered the live multimedia
stream. They may, after being provided with the trigger, and having
received a multicast address from the gateway in the exchange of second
multimedia session information, use IGMP to sign-up for the multicast.

[0029] In a further embodiment of the method the first multimedia stream
is a multicast stream. This is advantageous when the first transmitting
terminal has (received) a multicast address it can use to multicast its
multi-media stream.

[0030] In yet a further embodiment of the method, the first multimedia
stream is the same multimedia stream as the second associated multimedia
stream. In this case the (live) content may also be received live/without
any substantial delay from the transmitting first terminal. For enabling
additional trickplay (control) functionality, the transmitted multimedia
stream needs to be streamed and buffered first to a location under the
control of a multimedia server such as a RTSP server, before it is
retransmitted as a second associated stream to a second terminal. The
additional control functions (e.g. forward, backward, pause) may then be
exerted on this second associated stream.

[0031] In another embodiment of the method, the first terminal and the
gateway are both comprised in the same device and the first protocol is
an internal protocol. This may be an advantageous implementation when the
network (or studio/receiving-end) does not have the gateway functionality
according to the invention. Preferably this situation may occur when
there exist a one-to-one relationship between the transmitting and
receiving terminal, and both terminals are comprised in mobile devices.

[0032] In an aspect the invention relates to a system for transmitting a
multimedia stream from a first terminal and receiving an associated
second multimedia stream at a second terminal, wherein the system
comprises:

[0033] a first terminal and second terminal connected to at least one
gateway,

[0034] wherein the first terminal comprises (i) means for exchanging first
multimedia session information with the gateway, using a first protocol,
and (ii) means for transmitting a first multimedia stream;

[0035] wherein the gateway or first terminal comprises (iii) means for
triggering a second terminal, using a second protocol,--to initiate the
exchange of second multimedia session information between the second
terminal and the gateway, using a third protocol,

[0036] wherein the second terminal comprises (iv) means for receiving a
trigger, using a second protocol, and v) means for initiating the
exchange of second multimedia session information with the gateway in
response to said trigger, using a third protocol, and (vi) means for
receiving a second multimedia stream, associated with the first
multimedia stream;

[0037] In a further embodiment of the system according to the invention,
the gateway further comprises means for associating the first multimedia
session information to the second multimedia session information. This
may be advantageous, when the gateway does not have a default
configuration, how to instruct transmitting and receiving terminals, but
when a more flexible arrangement is required, whereby the setting
requests and capabilities of the terminals involved is taken into account
when setting up the multi-media sessions.

[0038] Yet another aspect of the invention relates to a gateway configured
for use in the system according to the invention, wherein the gateway
comprises:

[0039] means for exchanging first multimedia session
information with a first terminal, using a first protocol

[0040] means
for triggering the second terminal, the trigger being provided using a
second protocol, in response to which the second terminal is able to
initiate the exchange of second multimedia session information with the
gateway, and

[0041] means for exchanging second multimedia session
information with the second terminal, using the third protocol, the third
protocol being different from the first protocol

[0042] In a further embodiment of the gateway according to the invention,
the gateway further comprises means to associate the first multimedia
session information and the second multimedia session information with
each other

[0043] In yet a further embodiment of the gateway according to the
invention, the gateway comprises SIP client functionality and RTSP server
functionality.

[0044] In yet a further embodiment of the gateway according to the
invention, the gateway is embedded in an IMS network architecture,
wherein the first protocol is SIP, the third protocol is RTSP, and
wherein

[0045] means for exchanging first multimedia session
information are part of the Service Control Function within IMS

[0046]
means for the triggering of the second terminal are part of the Service
Control Function within IMS

[0047] means for exchanging second multimedia
session information are part of the Media Function within IMS

[0048] IMS is an architecture that is becoming more and more popular among
operators to be used for the provisioning of multimedia services to its
customers. The distributed gateway according to an embodiment of the
invention, is particular advantageous, because it may be implemented
using standard(ized) components and functionalities already present in
the IMS architecture.

[0049] In one embodiment of the invention a first terminal is connected to
a second terminal. Further, the first and second terminal are connected
to at least one gateway for enabling the multimedia stream to be
transmitted from the first terminal to the second terminal. The method
comprises the steps of: (i) the first terminal inviting the gateway to
set up a first multimedia session between the first terminal and the
gateway, the first multimedia session being controlled by a first
protocol; (ii) the gateway notifying--in response to the invitation--the
second terminal of the pending invitation; (iii) the second terminal
setting up--in response to the notification--a second multimedia session
between the second terminal and the gateway, the second multimedia
session being controlled by a second protocol; (iv) the gateway setting
up--in response to the invitation--the first multimedia session; and (v)
transmitting a multimedia stream from the first terminal to the second
terminal.

[0050] The method according to the embodiment thus allows the user of a
first terminal, which uses a first multimedia protocol, to stream
real-time user-generated content to a second terminal, which uses a
second multimedia protocol, where both the first and second terminal act
as a client.

[0051] In the method according to the embodiment a gateway is capable of
connecting a first terminal supporting a first protocol, e.g. SIP, to a
second terminal supporting a second protocol, e.g. RTSP. Towards the
first terminal, i.e. the (originating) SIP client at the user side, the
gateway acts as (terminating) SIP client. The gateway confirms that it is
able to receive the multimedia session from the user and provides first
terminal with multimedia session information. Towards the second
terminal, i.e. the RTSP client, the gateway acts as RTSP server on behalf
of the user, whereby the second terminal uses RTSP for session control.

[0052] The gateway informs the second terminal that an incoming session is
pending and notifies the RTSP client to connect to the RTSP server
function of the gateway.

[0053] The gateway thus acts as a server for both SIP and RTSP and uses a
notification message for connecting to the second terminal RTSP client.
This message acts as a trigger message and ensures that legacy SIP
clients from the user and RTSP clients from the studio can be connected
in order to enable user-generated content to be transmitted from the
first terminal to the second terminal.

[0054] In one embodiment the first protocol is the Session Initiation
Protocol (SIP). In a further embodiment the first terminal transmits an
SIP INVITE to the gateway.

[0055] In a further embodiment the second protocol is the Real Time
Streaming Protocol (RTSP).

[0056] In yet another embodiment the gateway transmits a notification
message to the second terminal in response to invitation of the first
terminal, in order to activate the second terminal to set up the second
multimedia session between the second terminal and the gateway.

[0057] In one embodiment the method comprises the steps of: --the first
terminal transmitting first multimedia session information to the
gateway; --the gateway transmitting the first multimedia session
information to the second terminal.

[0058] In another embodiment the method comprises the steps of: --the
second terminal transmitting second multimedia session information to the
gateway; --the gateway transmitting the second multimedia session
information to the first terminal. The first multimedia session
information and/or second multimedia session information is in a further
embodiment transmitted using the Session Description Protocol (SDP).

[0059] In yet another embodiment the first terminal comprises a SIP client
and/or the second terminal comprises an RTSP client.

[0060] In a further embodiment the invention relates to a method for
transmitting a multimedia stream from a first terminal to a second
terminal, wherein the first and second terminal are connected to a first
and a second gateway respectively. The gateways are capable of setting up
a multimedia session between the first and second terminal. The method
comprises the steps of: (i) the first gateway preparing the first
terminal for setting up a multimedia session with the second terminal,
wherein a first protocol is used for the preparation of the first
terminal; (ii) the first gateway inviting the second gateway to set up
the multimedia session between the first terminal and the second
terminal, the multimedia session being set up by a second protocol; (iii)
the second gateway notifying--in response to the invitation--the second
terminal to prepare the multimedia session with the first terminal
wherein the first protocol is used for preparation of the second
terminal; (iv) setting up--in response to the invitation--a multimedia
session between first terminal and the second terminal; and (v)
transmitting a multimedia stream from the first terminal to the second
terminal.

[0061] In this embodiment the purpose of the first SIP-RTSP gateway at the
user location and the second SIP-RTSP gateway at the studio location is
to exchange the correct RTP information (IP addresses, port number, SDP
session description, etc.) between the legacy SIP and RTSP functions.
This allows the RTP stream to be set-up and controlled by the SIP session
and enables the user to trigger the TV studio to retrieve the streamed
user-generated content. The RTSP protocol may be used to control the RTP
stream.

[0062] In one embodiment the first protocol may be the Real Time Streaming
Protocol (RTSP). In another embodiment the second protocol is the Session
Initiation Protocol (SIP).

[0063] In a further embodiment the second gateway transmits a notification
message to the second terminal in response to the invitation of the first
gateway, in order to activate the second terminal to set up the
multimedia session between the first terminal and the second terminal.

[0064] In one embodiment the method further comprises the steps of: --the
first gateway receiving first multimedia session information from the
first terminal using the SDP protocol encapsulated in the first protocol
and transmitting the first multimedia session information to the second
gateway using the SPD protocol encapsulated in the second protocol;
and--the second gateway receiving the first multimedia session
information from the first gateway and transmitting the first multimedia
session information to the second terminal using the SDP protocol
encapsulated in the first protocol.

[0065] In another embodiment the method further comprises the steps of:
--the second gateway receiving in response to the receipt of the first
multi media session information second multimedia session information
from the second terminal using the SDP protocol encapsulated in the first
protocol and transmitting the second multimedia session information to
the first gateway using the SPD protocol encapsulated in the second
protocol; --the second gateway receiving the second multimedia session
information from the second gateway and transmitting the second
multimedia session information to the first terminal using the SDP
protocol encapsulated in the first protocol.

[0066] The transmission of the multimedia stream from the first terminal
to the second terminal is in one embodiment controlled by the RTSP
protocol.

[0067] In a further embodiment the first terminal comprises a RTSP server
connected to the first gateway and/or the second terminal comprises an
RTSP client connected to the second gateway.

[0068] In a further aspect the invention relates to a system for
transmitting a multimedia stream from a first terminal to a second
terminal. In one embodiment the system comprises: a first terminal and
second terminal connected to at least one gateway, wherein the first
terminal comprises (i) means for inviting the gateway to set up a first
multimedia session with the first terminal, wherein the first multimedia
session is controlled by a first protocol and (ii) means for transmitting
a multimedia stream in the first multimedia session to the gateway; and
wherein the gateway comprises (iii) means for notifying--in response to
the invitation of the first terminal--to set up a second multimedia
session between the gateway and the second terminal, the second
multimedia session being controlled by a second protocol, (iv) means for
setting up--in response to the invitation--the first multimedia session
and (v) means for transmitting a multimedia stream to the second
terminal.

[0069] In a further embodiment a system is provided for transmitting a
multimedia stream from a first terminal to a second terminal. The system
comprises a first terminal and second terminal connected to a first and a
second gateway respectively. The gateways are capable of setting up a
multimedia session between the first and second terminal, wherein the
first gateway comprises: (i) means for preparing the first terminal for
setting up a multimedia session with the second terminal wherein a first
protocol is used for the preparation of the first terminal; (ii) means
for inviting the second gateway to set up the multimedia session between
the first terminal, the multimedia session being set up using a second
protocol;

wherein the second gateway comprises: (iii) means for notifying the
second terminal--in response to the invitation--to prepare the multimedia
session with the first terminal, wherein the first protocol is used for
the preparation of the second terminal and (iv) means for setting up--in
response to the invitation--a multimedia session between first terminal
and the second terminal.

[0070] In yet a further aspect the invention relates to a device
comprising a first terminal configured for use in the method according to
the invention, the device further comprising a gateway according to the
invention. This may be advantageous when the (operator) network does not
comprise or support a gateway according to the invention. The device may
for instance be a first mobile device wanting to offer a live stream to a
home computer reachable via the internet.

[0071] In another aspect of the invention a device is claimed, comprising
a second terminal configured for use in the method according to the
invention, the second terminal comprising:

[0072] means for receiving a
trigger, provided under the use of a second protocol

[0073] means for
initiating the exchange of second multimedia session information with the
gateway, in response to the providing of the trigger to the second
terminal, said initiating and exchange executed under the use of a third
protocol, said third protocol being different from said second protocol.

[0074] means for receiving a second multimedia stream associated to a
first multimedia stream

[0075] Preferably this device is configured in such a way that the second
terminal comprises a RTSP client and the third protocol used to initiate
the exchange of second multimedia stream session information, is the RTSP
protocol. This has the advantage that this device may now be able to
control the receipt of a multimedia stream and thereby use the available
trick play functionality provided by the RTSP protocol.

[0076] In a further aspect the invention also relates to a computer
program product comprising software code portions configured for, when
run in the memory of a terminal or gateway, executing the method steps
according to the invention.

[0077] The invention will be further illustrated with reference to the
attached drawing, which schematically show embodiments according to the
invention. It will be understood that the invention is not in any way
restricted to these specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0078] FIG. 1 illustrates an exemplary system in which the present
invention may be used.

[0079]FIG. 2 depicts a simplified exemplary flow of information using the
SIP protocol.

[0080]FIG. 3 depicts an exemplary flow of information using the RTSP
protocol.

[0082] FIG. 5a depicts the flow of information between a SIP client, a
SIP-RTSP gateway and a RTSP client in an exemplary embodiment of the
invention.

[0083] FIG. 5b depicts the flow of information between a SIP client, a
SIP-RTSP gateway and a RTSP client in another exemplary embodiment of the
invention.

[0084] FIG. 5c depicts the flow of information between a SIP client, a
SIP-RTSP gateway and a RTSP client in an exemplary embodiment of the
invention, whereby the first terminal and the gateway are both comprised
in a mobile device

[0085]FIG. 6 depicts an IMS architecture configured for use in the
invention.

[0086]FIG. 7 depicts the flow of information in an exemplary IMS
architecture configured for use in the invention.

DETAILED DESCRIPTION

[0087] FIG. 1 illustrates an exemplary system in which the present
invention may be used. At the home-location a first terminal 1, e.g.
comprised in a set-top box, is connected to display device, e.g. a
television. Further, the first terminal receives a TV signal 2, which is
broadcasted by the television studio and which comprises a program
providing live multimedia participation of home-located user. In one
embodiment the multimedia participation of the user may be realized using
e.g. a web-cam 3 connected to the terminal. The multimedia stream 4
generated by the web-cam is streamed over an IP network 5 to a second
terminal 6 located at the TV studio. At the TV studio the second terminal
6 receives the user-generated multimedia stream 4. This way a live video
feed from the user to the studio may be provided.

[0088] Such a service requires (i) a home-located user to be able to set
up a multimedia session between the home-located, first terminal 1 and
the second terminal 6 located at the studio, wherein the multimedia
session enables the streaming of user-generated multimedia content 4 to
the studio, and (ii) to enable the studio to control (e.g. play, pause,
stop) the multimedia stream sent by the home-located terminal.

[0089] It is understood that the system at the home location allowing
multimedia participation as described in connection with FIG. 1 may be
realized in various alternative ways. Those skilled in the art will
understand that the first terminal 1, the display device and the web-cam
may be for instance integrated in one device such as a personal computer,
a digital assistant (PDA), a mobile telephone with multi-media
capabilities. Similarly, the system at the studio may for example be a
media server comprising the second terminal, wherein the second terminal
comprises a RTSP client for multimedia stream retrieval. Alternatively,
the second terminal may be located in a mixer or a transcoder and
configured for multimedia stream adaptation.

[0090] In a further variant, the second terminal may be part of device,
that is located at another (home) location, and may be used for
user-to-user multimedia stream transmission. The device comprising the
second terminal may be a dedicated Set-Top Box (STB), a personal computer
or mobile phone containing media player software.

[0091] The first terminal may be regarded as a functional unit in a
device, or a device capable of managing (initiating, negotiating,
monitoring and controlling) the transmission of a multimedia stream.
Similarly, the second terminal may be regarded as a functional unit in a
device, or a device capable of managing (initiating, negotiating,
monitoring and controlling) the receipt of a multimedia stream.

[0092] In an IMS architecture the SIP protocol is used to set up and/or
negotiate a multimedia session between two SIP clients e.g. two IP
phones. Here, the term client may indicate a certain capability of a
device or terminal. For example a SIP client may refer to a device
configured for using the SIP protocol or to a terminal having SIP
capability.

[0093] An exemplary flow using the SIP protocol is depicted in FIG. 2.
Typically a first SIP client sends a SIP INVITE 7 to the second SIP
client, which in return accepts the invitation by transmitting a SIP 200
OK 8 message to the first SIP client. Both messages may carry information
about the multimedia session. This information is exchanged using the
Session Description Protocol (SDP), which may be encapsulated in the SIP
protocol. The multimedia session information may include amongst others
IP addresses, port numbers for the RTP streams, the type of media (voice,
audio, video, etc.) and codec information. Thereafter, multimedia may be
streamed between the SIP clients using the RTP protocol 9.

[0094] SIP however is designed for setting up and supporting interactive
media sessions. Although SIP also provides a form of aggregate streaming
control (i.e. the ability to control multiple streams from different
locations with one control session), it does not provide for an efficient
control as provided by the RTSP protocol used in streaming applications
such as Video on Demand (VoD). RTSP allows a client to remotely control a
streaming media (RTSP) server by issuing VCR-like commands e.g. play,
pause, stop, skip forward, skip backward etc. and allows time-based
access to files on a server. Moreover, legacy equipment may require the
use of RTSP, since legacy equipment may not be provided with a SIP
client.

FIG. 3 schematically depicts an exemplary flow using the RTSP protocol.
In setting up and controlling a RTSP multimedia session between an RTSP
client and an RTSP server, standard RTSP messages 10 (OPTIONS, DESCRIBE,
SETUP, PLAY) are exchanged between the client and the server in order to
provide both sides with information required for an RTSP session. The way
the RTSP protocol is designed to operate, it is always the RTSP client
and not RTSP server that initiates the set up of such a session. Similar
to SIP, RTSP session information is exchanged using the Session
Description Protocol (SDP), which may be encapsulated in the RTSP
protocol. Once the session is set up, multimedia may be streamed from the
server to the client 11, using the RTP protocol, wherein RTSP allows the
client to control the streaming.

[0095]FIG. 4 depicts a schematic view of a system representing an
exemplary embodiment according to the invention. In this embodiment a
home located first terminal 12 comprises a SIP client 13, which is
capable to set up a SIP session 14 with an SIP-RTSP gateway 15. The
SIP-RTSP gateway may be located in a device that may also comprise the
second terminal 16 at the TV studio. The second terminal 16 comprises a
RTSP client.

[0096] Towards the (originating) SIP client of the first terminal at the
user side, the gateway acts as a (terminating) SIP client. The gateway
confirms that it is able to receive the multimedia session from the first
terminal and informs the first terminal at the user side on the session
details and the RTP port number. This first multimedia stream session
information may be exchanged using the SDP protocol, which may be
encapsulated in the SIP messages.

[0097] The gateway may further be capable of resolving an identifier
received from the first terminal, used to identify the second terminal,
into a network address of the second terminal. The resolution process may
be performed by the gateway or under the control of the gateway by
another module. The identifier may already be a suitable network address
of the second terminal, in case of which the resolving is not required.

[0098] In response to the initiation of the exchange of first multimedia
stream session information, after being provided with a suitable network
address, the gateway may send a trigger message to the second terminal.
The trigger message instructs the RTSP client to initiate an RTSP session
with the gateway. The gateway does not have to send the trigger itself,
but may also instruct another module (such as a Short Message Service
Center SMSC) to do so on its behalf.

[0099] Hence, towards the second terminal comprising the RTSP client 18,
the SIP-RTSP gateway acts as an RTSP server, thereby allowing the RTSP
client to have RTSP session control over the RTP stream 19, which is
transmitted from the first terminal (SIP client) and received as an
associated second multimedia stream at the second terminal (comprising
the RTSP client).

[0100] The first multimedia stream may be the same multimedia stream as
the second associated multimedia stream. In that case content is streamed
directly from the first to the second terminal. The transmitted first
stream is not buffered under the control of a RTSP server before being
further transmitted as a second associated stream to the second terminal.
This has the advantage that the content is being presented in `live
modus` to the second terminal. In this modus the trickplay
functionalities (pause, fast forward etc.) of the RTSP client can not be
used to control the stream.

[0101]FIG. 5(a) illustrates an exemplary embodiment of the flow of
information between the SIP client (comprised in the first terminal), the
SIP-RTSP gateway and the RTSP client (comprised in the second terminal).
In a first step 20 the exchange of first multimedia stream session
information (SIP session) is initiated by the SIP client in the first
terminal, which sends an SIP INVITE to the gateway indicating that it
wants to stream a first multimedia stream to the second terminal. In
further variants, the first terminal may use another protocol to initiate
the exchange of first multimedia stream session information, such as
H.323 or MPEG-4 Delivery Multimedia Integration Framework (DMIF) Default
Signaling Protocol (DDSP).

[0102] In a second step 21 the gateway accepts the invitation and in
response, provides the second terminal with a trigger to start an RTSP
session with the SIP-RTSP gateway. Optionally, the gateway may first need
to resolve an identifier of the second terminal transmitted by the SIP
client in the first terminal, before it provides the trigger. The
resolving process to obtain the network address of the second terminal
may include a DNS, ENUM or other database query.

[0103] The gateway may add extra information to the trigger, such as a
gateway generated identifier, that can be used by the gateway to
associate the incoming RTSP request from the second terminal (the RTSP
request being part of the exchange of second multimedia stream session
information) with the SIP session. The information in the trigger may be
included in an RTSP URI.

[0104] The trigger may have the form of a trigger message, for example a
SIP content indirection request (RFC 4483), a Short Message Service (SMS)
message, or an Unstructured Supplementary Service Data (USSD) message.
Further, the trigger message may be passed to the RTSP client using a
proprietary application programming interface (API) or a control
interface on the RTSP client, for example a Web Service interface using
SOAP, a Remote Procedure Call (RPC), or a telnet interface. Such
interfaces may simulate a "manual user input" requesting a multimedia
stream.

[0105] The incoming trigger message may be interpreted by the trigger
protocol stack (for example an SOAP stack or RPC stack) which may be
configured to instruct the RTSP client to request a multimedia stream or
instruct another module to do so. Alternatively, the second terminal may
use another protocol to request a multimedia stream, such as Microsoft
Media Server protocol MMS, or Hypertext Transfer Protocol HTTP.

[0106] Thereafter, in a third step 22, the gateway handles the exchange of
second multimedia session information with the RTSP client comprised in
the second terminal, through transmitting the SDP information to the RTSP
client and retrieving from the RTSP client the correct RTP port to which
the RTP stream should be sent to. During this exchange the gateway give
instructions to the RTSP client, including for example the RTP port
number that should be used for receiving the (second associated)
multimedia stream or for example a multicast- or other address where the
stream can be retrieved from.

[0107] In a fourth step 23, the gateway confirms the SIP session to the
SIP client using a SIP 200 OK message and provides the SIP client with
the RTP port number, to be used for transmitting the first multimedia
stream and confirms the SDP information. Finally, in the fifth and last
step 24, the first terminal starts streaming the RTP multimedia stream to
the second terminal.

[0108] The termination of the combined SIP/RTSP session (not depicted in
FIG. 5(a)) may be handled in a similar way as the initiation of such
session described above. If the SIP client (of the first terminal)
indicates that it wants to terminate the session, the gateway may
translate an SIP BYE message into an RTSP REDIRECT message (without
location header). The RTSP REDIRECT message can be found in a draft of an
updated RTSP version (see Internet draft RFC 2326 version 16 of the Real
Time Streaming Protocol 2.0 dated 19 Nov. 2007 by Schulzrinne et al). If
the RTSP client (of the second terminal) indicates that it wants to
terminate the session, the gateway translates an RTSP TEARDOWN message
into a SIP BYE message (which is then subsequently to be sent to the SIP
client comprised in the first terminal)

[0109] In a further embodiment the streaming of multimedia may be first
initiated by the gateway. In that case the gateway provides the RTSP
client comprised in the second terminal with the trigger message and
invites through its own SIP client functionality the SIP client of the
first terminal to set up a SIP session. The flow of information between
the SIP client, the gateway and the RTSP client is schematically depicted
in FIG. 5(b).

[0110] In yet a further embodiment the gateway may be located in the first
terminal. In that case the first protocol, used for the exchange of first
multimedia stream session information may just be an internal protocol.
The session may then be triggered by a stimulus of the user interface of
the first terminal. This scheme is schematically depicted in FIG. 5(c),
wherein the first terminal may be comprised in a mobile device.
Alternatively, the stimulus received by the first terminal may also come
from an external source. In that case for example an SMS message received
by the mobile device may trigger a session.

[0111]FIG. 6 depicts an implementation of the invention in an IMS-based
IPTV architecture as defined by ETSI TISPAN. The architecture may for
example be used for a scenario, wherein a first subscriber of an IMS
based (user-generated) content service, commanding a first terminal (UE1
601), wants to stream his multimedia stream to a second subscriber,
commanding a second terminal (UE2 602).

[0112] In this embodiment the gateway according to the invention is of the
distributed type, wherein the exchange of first multimedia stream session
information with the UE1 is typically handled by the Service Control
Function (SCF 603) and the exchange of second multimedia stream session
information with the UE2 is handled by the Media Function (MF 605). The
provisioning of the trigger to the UE2 may be controlled and/or executed
by the SCF 603. In a variant, the Media Control Function 606 in the MF
can send the trigger and instruct the Media Delivery Function MDF 607 on
how to deliver the multimedia stream. In this example the first
subscriber uses SIP to setup a multimedia session for transmitting a
first multimedia stream, whereas the second subscriber uses RTSP to
receive the associated second multimedia stream.

[0113] In order for the first subscriber to invite the second subscriber
to receive the multimedia stream the following steps illustrated by the
flow diagram of FIG. 7 are performed. In a first step 701 a first
subscriber (using UE1 601) may want to share his multimedia stream with a
second subscriber (using UE2 602) by setting up a SIP session with the
Service Control Function SCF 603 through the IMS core 604. The SIP INVITE
request may comprise a list of subscriber terminal addresses, for example
using an URI-contained list, or a list may be sent to the Service Control
Function (SCF) outside the session, for example using XML Configuration
Access Protocol XCAP, of which an identifier may be included in the SIP
INVITE request. Alternatively, in case of a service such as Community
(closed user group) TV, in which a large number of subscribers need to be
addressed at once, the SIP INVITE request may just comprise a reference
to the community, in the form of a Community (closed user group)
Identifier, which will need to be resolved before providing multiple
triggers to all community subscribers.

[0114] In a second step 702 the SCF may act as a back-to-back user agent
(B2BUA) and sends a session request to the Media Control Function MCF
606, possibly through the IMS core. The session request to the MCF
includes information on where to receive the multimedia stream and how to
distribute it. Alternatively, the SCF may use another protocol towards
the MCF such as MEGACO/H.248 or SOAP.

[0115] In a third step the MCF may send multimedia stream information to
the MDF 607 to setup an RTP port and address for the first multimedia
stream and associate it with a RTSP URI. The MCF may for example use SIP
or MEGACO/H.248 to exchange multimedia stream information.

[0116] In a fourth step 704 the MCF response to the SCF may comprise
information such as the address or RTP port, where the first multimedia
stream should be transmitted to, and/or the RTSP URI to be used by the
UE2 for contacting the RTSP server functionality of the gateway.

[0117] In a fifth step 705 the SCF sends a response back to the UE1,
during the exchange of first multimedia stream session information, using
its SIP client functionality

[0118] In a sixth step 706 UE1 601 transmits the multimedia stream in the
manner and/or to the location indicated by the MCF.

[0119] In a seventh step 707 the SCF uses the information from the MCF to
provide a trigger to the UE2. The trigger may be a SIP content
indirection request. The request may include the RTSP URL provided by the
MF or another indication for the UE2 how to contact the gateway. The
trigger may also be sent within an existing SIP session with the UE2, or
by using a SIP REFER request.

[0120] In a eighth step 708 the invited UE2 602 initiates, in response to
the SIP content indirection request, a RTSP session with the MDF
(exchange of second multimedia stream session information, 708 in FIG. 7)
for receive the multimedia content (second associated multimedia stream
709). The RTSP URI may include an identifier provided in the trigger
message for the MDF to associate the RTSP session with the SIP session.
The RTSP session (second associated multimedia stream) may be unicast or
multicast. When multicast is used the MF distributes the incoming
(unicast) first multimedia stream of UE1 as a multicast stream. UE2 then
sends, in response to the established RTSP session, an IGMP request to
receive the second associated multimedia stream.

[0121] In a ninth step the MF may send SIP NOTIFY messages to the SCF to
keep the SCF informed of the status of the RTSP session, if the SCF
indicated interest by sending a SIP SUBSCRIBE message to the MF (not
shown in FIG. 7).

[0122] The invention is not limited to the embodiments described above,
which may be varied within the scope of the accompanying claims. For
instance, the term studio should not be interpreted as only meaning a
professional broadcast studio. A studio within the meaning of this
invention relates to all systems which could provide multimedia
functionality similar to a studio, e.g. a personal computer system or
another multimedia system which is capable of streaming live content to a
user at a home location and in response receiving user-generated content
from the user.